The invention concerns a method of making a cage for cylindrical rolling elements and more particularly, a needle roller cage for a mounting of an idler pinion in a toothed gear variable transmission, side rings of the cage being connected to each other by crossbars forming pockets, the crossbars being profiled so that the rolling elements are retained individually on both sides of the pitch circle by retaining edges extending parallel to axes of the rolling elements, the method comprising giving a sheet metal strip the desired profiled cross-section by chipless shaping forming the crossbars in the central region of the profiled strip by punching before the strip is bent round and, if necessary, connecting its abutting ends to each other.
A method of the pre-cited type for making such a cage is known from DE-OS 21 47 170. In this known method, a flat sheet metal strip is first given the desired cross-sectional profile by rolling, the pockets for the reception of the rolling elements are punched out either before or after the profiling and, finally, the strip is bent round and, if necessary, the abutting ends are welded to each other.
In such thin-walled, bent profiled cages of an M or W shape, the rolling element are retained by retaining edges arranged inside and outside of the pitch circle. The cages are made of thin-walled sheet metal because the small wall thickness enables a particularly economic fabrication of the pockets by punching. This however, has the drawback that punching fissures and generally rough punched surfaces are formed on the crossbars, i.e. the guide surfaces for the rolling elements are rough and imprecise on the whole. But rough surfaces when contacted by the needle rollers cause wear. Imprecise crossbar surfaces, in their turn, lead to axial thrust loading and axial abutting of the cage end faces against the axial limiting faces of the bearing under considerable surface contact pressure. The result of this in the case of the mounting of an idler pinion in mechanical transmissions can be that the idler pinion bearing is subject to considerable transverse or displacing forces and tends to wobble. Another drawback results from the fact that the pockets are punched out before the cage strip is bent round. In the finished cage, the pockets then present a V-shaped profile toward the center point of the bearing so that the danger of binding of the rolling elements exists.
The object of the invention is therefore to provide a method of making a profiled M or W cage in which the danger of lateral transverse or lateral displacing forces is reliably eliminated.
The invention achieves this object according to the characterizing part of Claim 1 by the fact that, by an additional shaping by material displacement after the punching out of the pockets, on the one hand, parallel opposing guide surfaces for the rolling elements are formed within the pitch circle between the retaining edges of the pockets, and on the other hand, the retaining edges on both sides of the pitch circle are dimensioned so that the distance between them in peripheral direction is only slightly smaller than the diameter of the rolling elements.
By this additional shaping step, also known to the person skilled in the art by the name of stamping, the cage pocket is pressed by material displacement into the shape required for a precise functioning of the cage. This means in the first place that the rolling elements are in contact with the cage in the region of the pitch circle and not, as was hitherto the case, inside or outside of the pitch circle. By this guidance in the region of the pitch circle which is achieved by the parallel guide surfaces of the pockets, the undesired transverse or displacing forces on the cage are avoided.
Another advantage of stamping is that the guide surfaces thus obtained are smooth and free of punching fissures and are additionally work-hardened at the same time. This prevents wear between the cage and the rolling elements. The exact contact of the rolling elements in the region of the pitch circle of the cage permits the use of a thicker starting strip, i.e. the stability of the cage is substantially enhanced.
A further advantage of stamping is that the retaining edges are dimensioned so that the distance between them is only slightly smaller than the diameter of the rolling elements. This allows a resilient displacement of the rolling elements into the pockets in the elastic region so that damage to the retaining edges or to the rolling surfaces of the rolling elements is reliably prevented.
Stamping is performed according to claim 2 in that one or more stamping tools are introduced into adjacent pockets and loaded by a force in peripheral direction so that the crossbar separating the two pockets is plastically deformed on both sides.
This is done in a known manner in that the crossbar is subjected to pressure its axial length from both sides by a stamping tool having a contour corresponding to the desired contour of the targeted guide surface and of the retaining edges of the crossbar. These stamping tools are then moved toward each other in peripheral direction so that a plastic displacement of material takes place in the region of the crossbar. A detailed description of this stamping procedure, known, per se, is not required here because its use with solid cages is already known and has been described in detail, for example, in DE-AS 11 45 126.
The invention will now be described more closely with reference to the following example of embodiment.